what does this universal ctags error mean: Don't reuse the kind letter

Question

Since universal-stags doesn't support swift out of the box, I added this to my ~/.ctags.d/ctags.ctags:

--langdef=Swift
--langmap=Swift:+.swift
--regex-swift=/(var|let)[ \t]+([^:=<]+).*$/\2/,variable/
--regex-swift=/func[ \t]+([^\(\)<]+)\([^\(\)]*\)/\1/,function/
--regex-swift=/class[ \t]+([^:\{<]+).*$/\1/,class/
--regex-swift=/struct[ \t]+([^:\{<]+).*$/\1/,struct/
--regex-swift=/protocol[ \t]+([^:\{<]+).*$/\1/,protocol/

But when I run the command

ctags . -R

I get this weird warning

ctags . -R
ctags: Warning: Don't reuse the kind letter `r' in a language Swift (old: "variable", new: "function")
ctags: Warning: Don't reuse the kind letter `r' in a language Swift (old: "variable", new: "class")
ctags: Warning: Don't reuse the kind letter `r' in a language Swift (old: "variable", new: "struct")
ctags: Warning: Don't reuse the kind letter `r' in a language Swift (old: "variable", new: "protocol")

and my tags file doesn't get updated. Interestingly enough, if I run this command

ctags --languages=swift -R .

I still get the same warning, but my tags file does get updated.

What does this warning even mean and how do I get rid of it?

Answer 1

You specified kind names for patterns like ,variable, ,function. However, you didn't specify kind letters, single characters representing kinds. If a kind letter is omitted, r is used as default; ctags handled ,variable as r,variable. When ctags read ,function, ctags assumed the user wanted to use r as a kind letter for the kind named "function". However, r was already used for the kind named "variable". ctags warned of this conflict.

Specifying kind letters may suppress the warnings:

--langdef=Swift
--langmap=Swift:+.swift
--regex-swift=/(var|let)[ \t]+([^:=<]+).*$/\2/v,variable/
--regex-swift=/func[ \t]+([^\(\)<]+)\([^\(\)]*\)/\1/f,function/
--regex-swift=/class[ \t]+([^:\{<]+).*$/\1/c,class/
--regex-swift=/struct[ \t]+([^:\{<]+).*$/\1/s,struct/
--regex-swift=/protocol[ \t]+([^:\{<]+).*$/\1/p,protocol/

Universal-ctags introduced --kinddef-<LANG>= option. I recommend you to use the option.

--langdef=Swift
--langmap=Swift:+.swift
--kinddef-Swift=v,variable,variables
--kinddef-Swift=f,function,functions
--kinddef-Swift=c,class,classes
--kinddef-Swift=s,struct,structs
--kinddef-Swift=p,protocol,protocols
--regex-swift=/(var|let)[ \t]+([^:=<]+).*$/\2/v/
--regex-swift=/func[ \t]+([^\(\)<]+)\([^\(\)]*\)/\1/f/
--regex-swift=/class[ \t]+([^:\{<]+).*$/\1/c/
--regex-swift=/struct[ \t]+([^:\{<]+).*$/\1/s/
--regex-swift=/protocol[ \t]+([^:\{<]+).*$/\1/p/